1). Field of the Invention
The present invention relates to converting a video signal comprising input image samples conforming to an interlace scanning lattice into a video signal comprising output image samples conforming to a progressive scanning lattice.
2) Description of the Related Art
Image transmission systems require an initial generation of a multidimensional signal which is a function of three independent variables (x,y,t) in space and time. The initial signal is sampled and formatted so as to form a one-dimensional signal suitable for transmission. The sampling operation can be described by a sampling lattice which expresses the sample locations as a linear combination of sample indices which are the horizontal, temporal and vertical indices respectively. The two most common lattices used in transmitting video signals are the progressive scanning lattice and the interlace scanning lattice.
Considerable attention has been paid to providing higher quality pictures for television picture transmissions and the possibility for conversion between different sampling lattices. Such conversion requires attention to the conversion of video signals which employ an interlace scanning lattice into video signals which conform to a progressive scanning lattice.
A problem with such conversion arises because of the generation of unwanted image artefacts.
It is an aim of the present invention to provide improved filtering in the conversion of a video signal from an interlace scanning lattice to a progressive scanning lattice.
According to the present invention there is now provided a method of converting a video signal comprising input image samples conforming to an interlace scanning lattice into a video signal comprising output image samples conforming to a progressive scanning lattice, the method comprising the steps of: applying the input image samples to first and second temporal filters to divide the input image samples into first and second temporal sub-bands; vertically filtering each temporal sub-band by means of a low-pass vertical filter; the higher temporal sub-band being vertically filtered to a greater degree than the lower temporal sub-band; and, recombining the filtered image samples from each sub-band to form a filter output signal.
Further according to the present invention, there is provided apparatus for converting a video signal comprising input image samples conforming to an interlace scanning lattice into a video signal comprising output image samples conforming to a progressive scanning lattice, the apparatus comprising: first and second temporal filters to receive and divide the input image samples into first and second temporal sub-bands; first and second low-pass vertical filters to vertically filter each temporal sub-band such that the higher temporal sub-band is vertically filtered to a greater degree than the lower temporal sub-band; and, recombining means to recombine the filtered image samples from each sub-band to form a filter output signal.